Delayed Hemolytic Transfusion Reaction

By definition, occurs 24 hours or more after transfusion, usually within 2 weeks

Due to anamnestic immune response in patients previously alloimmunized by certain RBC antigens; hemolysis is usually extravascular

Cannot be detected by pretransfusion antibody screening tests or crossmatches because antibodies are present in low concentrations, have low affinity for antigen or indicator antigen is missing from test red cells

Antibodies are usually IgG reactive at 37°C, fix complement; Duffy (Fya) and Kidd (Jka) are most likely

Associated with prolonged intervals between initial and subsequent transfusions, as antibodies decrease to undetectable levels

Rarely is due to a primary immune response with no prior exposure (Immunohematol 2004;20:184)

Sickle cell patients usually have non-severe symptoms (Transfusion 2002;42:37), but may have acute pain syndrome with life threatening anemia due to bystander hemolysis (hyperhemolysis, Pediatrics 2003;111:e661)